Without limiting the scope of the invention, its background is described in connection with existing methods and apparatus for guiding and confirming proper placement of medical apparatus that are inserted through a body channel or cavity.
Medical diagnosis and treatment frequently involve insertion of medical devices that are passed through naturally occurring channels and cavities in the patient's body. These include placement of catheters into large blood vessels such as through jugular, subclavian, antecubital and femoral sites. Cardiac catheterization involves passage of long catheters from peripheral insertion sites into the heart using X-ray visualization. Catheterization is also used to access the bladder and kidneys by retrograde passage through the urethra. Placement of nephrostomy tubes is typically done percutaneously into the renal pelvis under fluoroscopic or CT guidance. In any interventional procedure, insertion of the medical device into the proper location is critical. For example, improper placement or positioning of an endotracheal tube may be lethal.
Correct placement and positioning of an endotracheal tube is an essential component of life support during resuscitation from cardiac arrest, during stabilization and surgery after severe multiple trauma, during critical illnesses requiring airway and ventilatory support, during most surgical procedures under general anesthesia and during postoperative mechanical ventilatory support. To function properly in ventilating the lungs, an endotracheal tube must be inserted into the trachea, must be properly positioned in the mid-trachea and must remain properly positioned until the endotracheal tube is no longer necessary. However, endotracheal tubes are often misplaced, particularly when placed in emergency circumstances, and endotracheal tube misplacement contributes to morbidity and mortality. Katz and Falk (Katz S H, Falk J L: “Misplaced endotracheal tubes by paramedics in an urban emergency medical services system” Ann. Emerg Med. (2001) 37:32-7) reported on a series over an eight-month interval of 108 patients who were intubated by emergency medicine personnel before arrival at a single-hospital Emergency Department (ED). On arrival at the ED, 25% (27/108) of endotracheal tubes were misplaced. Eighteen of 27 were in the esophagus; of those 18 patients, 56% died in the ED. In nine of the 27 endotracheal tubes were too deep (below the carina) or remained in the hypopharynx above the vocal cords; of those patients, 33% died in the ED. Li (Li J: “Capnography alone is imperfect for endotracheal tube placement confirmation during emergency intubation” J. Emerg. Med. (2001) 20:223-9) reported data, provided by the National Emergency Airway Registry database, regarding emergency endotracheal intubation performed in 24 participating hospital EDs from August 1997 to September 1999. Of 4,602 attempted emergency endotracheal intubations, the number of inadvertent esophageal intubations was 180, representing 4% of emergency intubations. Of these, ten (6% of all esophageal intubations) were initially unrecognized.
Misplacement of an endotracheal tube contributes to morbidity and mortality in several ways. Placement in the esophagus rather than in the trachea results in failure to effectively provide oxygen and remove carbon dioxide. Even a single breath administered while a tube is improperly positioned in the esophagus risks gastric inflation and promotes regurgitation and aspiration of gastric contents. Positioning of an endotracheal tube insufficiently far into the trachea risks laryngeal damage from cuff pressure on the structures in the larynx and, of greater immediate concern, risks accidental withdrawal into the pharynx. Positioning of an endotracheal tube too deeply may result in intubation of a main-stem bronchus, usually the right, causing hypoxemia because of failure to ventilate the opposite, usually the left, lung. Even a properly positioned endotracheal tube may subsequently move during taping (used to secure the endotracheal tube), retaping or changes in patient position. Misplacement after initial presumed placement most commonly occurs in obese patients, females, children and patients undergoing laparoscopy or placement in the Trendelenburg (head-down) position. See e.g. Weiss M, et al. “Clinical evaluation of cuff and tube tip position in a newly designed paediatric preformed oral cuffed tracheal tube” Br. J. Anaesth. (2006) 97:695-700. Because misplacement of an endotracheal tube can be lethal, proper positioning must be confirmed immediately after initial placement and must subsequently be monitored so that later tube displacement can promptly be recognized and corrected.
Proper insertion and positioning of endotracheal tubes is customarily performed or supervised by the most expert individual available, but expertise in endotracheal tube placement and maintenance varies widely by training and location. For respiratory support during surgery, placement is usually performed by anesthesiologists or nurse anesthetists, who typically are highly experienced and intubate patients on a daily basis. Moreover, during elective surgery, the risk is further reduced because most elective surgical patients have relatively good physiological reserves, surgical precautions reduce the risk of aspiration, and intubation is performed in highly controlled, nonemergency circumstances.
In hospitalized patients outside the surgery suite, endotracheal tube placement is usually performed as an emergency life-support procedure by a variety of physicians and nonphysicians, depending on the size and complexity of a hospital. Patients requiring emergency intubation usually have severe physiologic compromise, such as respiratory failure and cardiac arrest, and often must be intubated under poorly controlled circumstances by personnel with highly variable experience and expertise. These patients are particularly vulnerable to episodic hypoxemia. In EDs, placement is usually performed by emergency physicians, some of whom have considerable training, experience and expertise. However, some do not. In smaller hospitals during night shifts and on weekends, endotracheal tube placement is often performed by respiratory therapists, whose training varies widely and who may rarely have the opportunity to practice intubation.
In out-of-hospital situations, placement is usually performed by emergency medicine technicians or paramedics, whose experience and training often are limited. The inevitable disparities in experience and expertise between ED physicians, respiratory therapists, anesthesiologists and out-of-hospital emergency responders are compounded in emergency circumstances by less than optimal conditions and limited monitoring equipment. These important factors further reduce the chances of proper initial placement and subsequent maintenance of proper positioning of endotracheal tubes.
After endotracheal tube placement before surgery, patients subsequently remain in a highly monitored, stable environment, in which endotracheal tube position can be constantly monitored by an anesthesiologist or nurse anesthetist who can recognize tube displacement and intervene. Patients who are endotracheally intubated outside surgical suites or outside hospitals typically must be transported to other locations for definitive therapy, diagnostic imaging or intensive care. In each environment and during transport, because misplacement of an endotracheal tube can be lethal, proper positioning must be confirmed immediately after initial placement and must subsequently be monitored so that later tube displacement can promptly be recognized and corrected. Currently available technology is unsuitable for monitoring of endotracheal position, especially by personnel of limited experience.
The current gold standards of clinical practice for confirmation of endotracheal tube position include: (1) direct visualization of the endotracheal tube entering the trachea, (2) auscultation to confirm bilateral, symmetrical breath sounds and absence of air entry over the epigastrium (to exclude esophageal intubation), (3) detection of exhaled carbon dioxide to confirm placement in the lungs, (4) fiberoptic confirmation by visualization of the trachea and mainstem bronchi, and (5) chest radiography. Of these techniques, only fiberoptic airway examination and chest radiography provide direct information of proper positioning in the mid-trachea.
Salem (Salem M R. “Verification of endotracheal tube position” Anesthesiol. Clin. North America (2001) 19:813-39) has summarized the pitfalls of each of these techniques. Although each is relatively reliable, each also is associated with errors, the consequences of which can be grave. In some patients, visualization of the larynx is inadequate to confirm endotracheal tube placement. Direct visualization of an endotracheal tube passing the cords requires expertise in laryngoscopy, is sometimes difficult or impossible to achieve, and cannot be performed repeatedly. Fiberoptic bronchoscopy requires technical expertise, interferes with ventilation, and cannot be performed continuously. Chest radiography is intermittent, requires movement of a patient to perform radiography, and does not provide rapid feedback.
Auscultation is prone to both false-positive and false-negative findings. The dramatic decrease in respiratory complications of anesthesia during the past thirty years is certainly attributable in part to expeditious recognition and correction of esophageal intubation, although anesthesia personnel continue to be challenged by difficulty in confirming endotracheal tube placement in the mid-trachea, especially in circumstances in which post-intubation movement of a patient can result in movement of the tube within the trachea.
The challenges of recognizing esophageal intubation and endotracheal tube movement are much greater in emergency circumstances outside the operating room. Detection of exhaled carbon dioxide by capnography functions well in physiologically stable patients during surgical anesthesia. However, in emergency circumstances, especially during cardiac arrest, capnography is less reliable because carbon dioxide exhalation is highly variable and requires ventilation. In patients during cardiac arrest, minimal carbon dioxide may be exhaled through the lungs and use of this method provides a substantial incidence of false-positive and false-negative results in emergency intubations. Li quantified the sensitivity and specificity of capnography when used in emergency circumstances. (Li J: supra) Based on a meta-analysis of capnography trials that included 2,192 intubations, the sensitivity for confirmation of endotracheal intubation was 93% (95% confidence interval 92-94%), and the specificity was 97% (CI 93-99%). Therefore, for emergency intubations, the false-negative failure rate (tube in trachea but capnography indicates esophagus) was 7%, and the false-positive rate (tube in esophagus but capnography indicates trachea) was 3%.
To address the clinical problems of promptly recognizing initial endotracheal tube misplacement or subsequent endotracheal tube displacement, a variety of technological aids have been suggested or developed to supplement or replace auscultation and quantitative capnography. See e.g. O'Connor C J, et al. “Identification of endotracheal tube malpositions using computerized analysis of breath sounds via electronic stethoscopes” Anesthesia and Analgesia (2005) 101:735-9; Cardoso M M, et al. “Portable devices used to detect endotracheal intubation during emergency situations: a review” Crit Care Med. (1998) 26:957-64; Ezri T, et al. “Use of the Rapiscope vs chest auscultation for detection of accidental bronchial intubation in non-obese patients undergoing laparoscopic cholecystectomy” J Clin. Anesth. (2006) 18:118-23; Reicher J, et al. “Use of radio frequency identification (RFID) tags in bedside monitoring of endotracheal tube position” J Clin. Monit. Comput. (2007) 21:155-8; Werner S L, et al. “Pilot study to evaluate the accuracy of ultrasonography in confirming endotracheal tube placement” Ann. Emerg Med. (2007) 49:75-80; Li J. “A prospective multicenter trial testing the SCOTI device for confirmation of endotracheal tube placement” J Emerg Med. (2001) 20:231-9; and Milling T J, et al. “Transtracheal 2-D ultrasound for identification of esophageal intubation” J. Emerg. Med. (2007) 32:409-14).
The principles of operation of the devices vary. Some qualitatively detect exhaled carbon dioxide, some utilize transmission of light from within the trachea to the skin surface, some depend on aspiration of air from the trachea, and some are based on ultrasonography. The Sonomatic Confirmation of Tracheal Intubation (SCOTI) device connects to the end of the endotracheal tube and assesses the air content of the structure within which the endotracheal tube is located, i.e., within the rigid, air-filled trachea or the flaccid esophagus. However, the SCOTI device requires disconnection from the ventilator, only differentiates esophageal from tracheal intubation, has an appreciable false-positive and false-negative rate and does not indicate proper position within the trachea. Ultrasound-based techniques require expertise in ultrasonography and are not suitable for continuous monitoring.
Although all approaches offer advantages and provide feedback that can be helpful, no single device is sufficiently reliable to be considered the standard of care and some, such as fiberoptic bronchoscopy, require substantial skill and training.
Thus, there is a real need in the art for an easy method for monitoring and confirming proper placement of indwelling medical apparatus in a mammalian body including a human body.